Straight women are open to having lesbian sex and their men don't mind!

A new theory suggests that women may have been evolutionarily designed to be sexually fluid. So, if you are a girl and like to have sex with your male partner one day and a female pal the next, you may not be alone.

The theory has been postulated by researchers at a leading London institute, who say that women can change their sexual desires and identities from lesbian, to bisexual, to heterosexual and back again.

Female sexual fluidity may have evolved as an adaptation to facilitate polygynous marriages, in which a husband can have more than one wife. In evolutionary terms, sexual fluidity allowed them to have sex with their co-wives in polygynous marriages, therefore, reducing conflict and tension inherent in such marriages while at the same time successfully reproducing with their husbands in heterosexual unions, the research revealed.

The theory may also help explain why men enjoy watching lesbian sex, and a number of puzzles in human sex research, including differences in female and male homosexuality, and menstrual synchrony.

Slept with another woman? Men don't care!A study conducted by psychologists at an American university found that men are more than twice as likely to continue dating a girlfriend who has cheated on them with another woman than one who has cheated with another man.

Conversely, women are more likely to continue dating a man who has had a heterosexual affair than one who has had a homosexual affair. The study provides new insight into the psychological motivation behind men's desire for a variety of partners and women's desire for a committed partner.

Researchers asked 700 college students to imagine they were in a committed romantic and sexual relationship with someone they've been dating for three months. They were then asked how they would respond to infidelity committed by the imagined partner.